siRNA4⁺ EBV-CTLs retain their function in vivo in the presence of FK506. To evaluate in vivo antitumor activity, irr-siRNA⁺ and siRNA4⁺ EBV-CTLs were injected intraperitoneally in SCID mice bearing EBV⁺ lymphoma labeled with FFLuc. EBV-CTLs were transferred 4 and 11 days after intraperitoneal tumor implant. Tumor growth was monitored using the IVIS in vivo imaging system. IL-2 and FK506 were injected intraperitoneally 3 times per week. (A) By 33 days after CTL infusion, tumor growth, measured as maximum photon/sec/cm²/steradian (p/s/cm²/sr), was significantly greater in mice receiving irr-siRNA⁺ EBV-CTLs and FK506 compared with mice (8 mice per group) receiving siRNA4⁺ EBV-CTLs and FK506. Lines represent the average light emission ± SD. (B) Pictures of 4 representative mice per group. (C) The survival curve for SCID mice bearing EBV⁺ lymphoma that received irr-siRNA⁺ or siRNA4⁺ EBV-CTLs and IL-2 and FK506 intraperitoneally 3 times/week. Control mice received irr-siRNA⁺ or siRNA4⁺ EBV-CTLs and IL-2 but not FK506.